The present invention relates to angioplasty and, in particular, to perfusion balloon angioplasty catheters.
Balloon catheters are widely used in a variety of intravascular applications. In particular, angioplasty has gained wide acceptance as an efficient and effective treatment for particular vascular conditions. For example, angioplasty is widely used to treat stenoses in coronary arteries, although its application to stenoses in other parts of the vascular system is also known.
The most common form of angioplasty is percutaneous translumenal coronary angioplasty (PTCA) which utilizes a dilatation catheter having an inflatable balloon at its distal end. The catheter is guided through the vascular system, using fluoroscopy, until the balloon is positioned across the stenosis. The balloon is then inflated such that the balloon engages the stenosis to reestablish acceptable blood flow through the artery.
An initial concern with PTCA was the temporary blockage of blood flow during balloon inflation. With increasing clinical experience, this concern declined. The vast majority of patients tolerate 30-60 second dilatations quite well. Concurrently, cardiologists discovered that prolonged dilatations can assist with some developments occasionally encountered with angioplasty. For example, prolonged dilatations of several minutes may be employed on the occurrence of dissections, intimal flaps, acute thrombolysis and vessel spasms. The profound ischemia of long dilatation is outweighed by the potential prevention of emergency coronary bypass surgery.
A variety of techniques have been proposed to facilitate prolonged dilatations. These include the use of pharmacologic agents to improve myocardial tolerance of ischemia, synchronized retroperfusion, mechanical pump distal perfusion and auto or passive perfusion.
The use of pharmacologic agents treats the symptoms of ischemia without addressing the cause. As a result, this approach is inherently limited.
Synchronized retroperfusion involves pumping blood during diastole into the coronary sinus and then subselectively into the regional coronary veins which drain the jeopardized myocardium. While this approach potentially offers nearly complete myocardial perfusion, it is complicated and cumbersome. Mechanical pump distal perfusion involves pumping blood (or other perfusate) through a lumen of the PTCA catheter. As the name implies, this requires some form of mechanical pump which complicates the angioplasty equipment and procedure.
Auto or passive perfusion has found increasing interest both for prolonged dilatations as well as shorter dilatations having a duration on the order of non-perfusion dilatations. Typically, in passive perfusion, the balloon catheter acts as temporary stent. That is, a perfusion lumen is employed to provide a blood flow passage during balloon inflation. Typically, the perfusion lumen extends through the balloon envelope having an inlet proximal to the balloon envelope and a discharge distal to the balloon envelope. Proposed inlet configurations have included side openings in the catheter as well as a beveled opening to the blood flow channel. Proposed discharge configurations have included a main axial orifice and side openings. Clearly, the inlet and outlet have a direct effect on blood flow capacity. Further, pressure within the balloon envelope during balloon inflation has a tendency to compress a perfusion lumen within the envelope thereby potentially constricting the blood flow passage. On the other hand, countering this tendency by stiffening the perfusion lumen walls can seriously impact trackability of the catheter itself. The attachment of a projecting distal tip to provide side wall discharge can affect trackability as a result in changes of stiffness from material changes and/or the attachment itself.
As discussed above, various proposed discharge configurations have included a main axial orifice and side openings. For a number of reasons, including trackability, it is desirable to be able to control relative egress flow through the main axial orifice and the side openings. Such control can increasingly be a factor when perfusion flow is maximized, for example, where the guide wire along which the catheter is inserted is withdrawn after catheter insertion in order to increase the cross-sectional flow area through the perfusion lumen of the catheter which passes through the balloon envelope.
It is to these dictates of the prior art that the present invention is directed. It is a balloon angioplasty catheter which serves to obviate many of the shortcomings of prior art structures.